Fluidized process for improved stripping and/or cooling of particulate spent solids, and reduction of sulfur oxide emissions

Abstract

A fluidized process which comprises contacting a hydrocarbon feedstock with a fluidized particulate solid in a contacting zone wherein carbonaceous deposits accumulate on the solid and the solid becomes spent and wherein the carbonaceous deposits are burned from the spent solid to produce a regenerated solid; removing a stream of the fluidized spent solid and entrained hydrocarbons from the contacting zone; introducing the fluidized spent solid/entrained hydrocarbon stream and a stream of hot regenerated solid into a lower portion of a zone; introducing a stream of a fluid stripping medium, e.g, water and/or steam into the lower portion of the stripping zone to contact the spent solid therein; passing a stream of the spent solid mixed with the stripping medium and the hot regenerated solid upwardly in the stripping zone to an upper portion thereof under dilute phase stripping conditions; separating the spent solid from the hydrocarbons and stripping medium in a separation zone connected to the upper portion of the stripping zone; passing a fluidized stream of separated solid from the separation zone to the regeneration zone wherein said carbonaceous deposits are burned therefrom to produce a regenerated solid for return to the reaction zone; removing a stream containing vaporized separated hydrocarbons and stripping medium from the separation zone; separating the vaporized separated stripping medium from the hydrocarbons; recycling the separated stripping medium to the stripping zone. The process also contemplates introducing the medium into a lower portion of a dilute phase zone to cool the solid.

What is claimed is: 
     
       1. In a fluidized process which process comprises contacting a hydrocarbon feedstock with a fluidized particulate solid in a contacting zone wherein carbonaceous deposits accumulate on the solid and the solid becomes spent and the resulting spent solid is passed to a regeneration zone wherein said deposits are removed from the spent solid by firing to form a regenerated particulate solid, the improvement comprising: (a) removing a stream of the spent solid and entrained hydrocarbons from the contacting zone;   (b) removing a stream of hot regenerated solid from said regeneration zone;   (c) introducing the spent solid/entrained hydrocarbon stream and said hot regenerated solid stream into a lower portion of an elongated dilute phase stripping zone;   (d) introducing a stream of a fluid stripping medium into the lower portion of the stripping zone to contact the resulting mixture of spent solid and regenerated solid therein;   (e) passing a stream of the spent solid/entrained hydrocarbon mixed with the hot regenerated solid and stripping medium upwardly in the stripping zone under dilute phase stripping conditions to an upper portion thereof;   (f) separating substantially all of the spent solid and regenerated solid from the hydrocarbons and stripping medium in a separation zone connected to the upper portion of the stripping zone to produce separated solids substantially free of hydrocarbons;   (g) passing a fluidized stream of the separated solids substantially free of hydrocarbons from the separation zone to the regeneration zone;   (h) removing a stream containing vaporized separated hydrocarbons and stripping medium from the separation zone;   (i) separating the vaporized separated hydrocarbons from the stripping medium; and   (j) recycling the separated stripping medium to the stripping zone.   
     
     
       2. The process of claim 1, wherein said process is a fluidized catalytic cracking process and said particulate solid is a fluidizable cracking catalyst. 
     
     
       3. The process of claim 1, wherein said stripping medium is a fluid selected from the group consisting of steam, water, sour water and mixtures thereof. 
     
     
       4. The process of claim 1, wherein said solid returned to said regeneration zone is substantially free of fines. 
     
     
       5. The process of claim 1, wherein said separation zone comprises one or more cyclone separators. 
     
     
       6. The process of claim 3, wherein said separated stripping medium is heat exchanged with boiler feed water to produce steam. 
     
     
       7. The process of claim 3, wherein said separated stripping medium is heat exchanged with condensed separated stripping medium to produce superheated stripping medium for recycle back to the lower portion of said contacting zone. 
     
     
       8. The process of claim 7, wherein said condensed stripping medium is treated to remove solid fines therefrom before being vaporized. 
     
     
       9. The process of claim 1, wherein said stripping medium is water and said water cools said spent solid to increase the solid to hydrocarbon ratio in said contacting zone. 
     
     
       10. The process of claim 1, wherein the residence time of said solid in said stripping zone is less than 10 seconds. 
     
     
       11. The process of claim 10, wherein said residence time is less than 4 seconds. 
     
     
       12. The process of claim 1, wherein the superficial velocity of said solid in said stripping zone is less than 120 fps. 
     
     
       13. The process of claim 1, wherein the density of the fluidized stream in said stripping zone is less than 15 pounds per cubic foot. 
     
     
       14. The process of claim 1, wherein said stripping zone is an elongated, vertical vessel. 
     
     
       15. The process of claim 2, wherein the weight ratio of the regenerated catalyst to hydrocarbon feedstock in said contacting zone is greater than 10 weight parts of catalyst per weight part of hydrocarbon. 
     
     
       16. The process of claim 2, wherein the temperature of the regenerated catalyst is less than 1350° F. 
     
     
       17. The process of claim 2, wherein the temperature of the regenerated catalyst is less than 1250° F. 
     
     
       18. The process of claim 1, wherein the temperature within said stripping zone is greater than 1000° F. 
     
     
       19. The process of claim 1, wherein said stream containing separated hydrocarbons and stripping medium removed from said separation zone contains at least 50 weight % of any sulfur compounds on said spent solid removed from said contacting zone. 
     
     
       20. The process of claim 3, wherein said stripping medium is introduced into said stripping zone at a rate greater than 3 pounds per 1,000 pounds of spent solid. 
     
     
       21. In a fluidized process which process comprises contacting a hydrocarbon feedstock with a fluidized particulate solid in a contacting zone wherein carbonaceous deposits accumulate on the solid and the solid becomes spent and the resulting spent solid is passed to a regeneration zone wherein said deposits are removed from the spent solid by combustion to form a hot regenerated particulate solid, the improvement comprising: (a) removing a stream of the spent solid from the contacting zone;   (b) removing a stream of hot regenerated solid from said regeneration zone;   (c) introducing the spent solid and hot regenerated solid streams into a lower portion of a vertical elongated dilute phase stripping zone;   (d) introducing a stream of a fluid cooling medium into the lower portion of the elongated dilute phase zone to contact and cool the resulting mixture of spent solid and hot regenerated solid therein;   (e) passing a stream of said resulting mixture of solids and cooling medium upwardly in the elongated dilute phase stripping zone to an upper portion thereof;   (f) separating substantially all of the spent and regenerated solids from the cooling medium in a separation zone connected to the upper portion of the dilute phase zone to produce a cooled solid;   (g) passing a fluidized stream of the cooled separated solid from the separation zone to the regeneration zone; and   (h) removing a stream containing vaporized separated cooling medium from the separation zone.   
     
     
       22. The process of claim 21, wherein the cooling medium is water, steam or a mixture thereof. 
     
     
       23. The process of claim 22, wherein the vaporized medium is condensed and recycled to the dilute phase zone.